A gas sensor measures the density of specific gas, and is classified into a semiconductor gas sensor, a contact combustion gas sensor, and an electrochemical gas sensor, etc. From among the above-mentioned gas sensors, the semiconductor gas sensor measures the influence of resistance changed when a target material to be measured is oxidized or reduced, and the electrochemical gas sensor measures the amount of ions generated by oxidizing/reducing gas dissolved in electrolyte so that it can measure the density of gas.
Since most gas other than inert gas has a tendency of oxidation-reduction, the semiconductor gas sensor and the electrochemical gas sensor unavoidably generate crosstalk in which target gas to be measured and other gases are simultaneously measured. Therefore, there is a limitation in measurement selectivity through which specific gas can be selectively measured.
In addition, whereas the olfactory organ of a human being can sense a ppb-level gas emitting a smell, the measurement sensitivity of a conventional gas sensor is less than that of the human olfactory organ, so that the conventional gas sensor has difficulty in measuring gas of a ppm level or lower.